2.4.4 - The ratio of the forces.

The attraction exerted by the Earth, on the water of its oceans, is about 9 million times more than that exerted by the Moon on the same waters.


prologue > index tides > 2.4 Confrontation on the tides.

2.4.1 Confrontation on the tides - introduction.
2.4.2 Two different descriptions of the tides.
2.4.3 The physical formula valid for the tides.
The ratio of the forces.
Number of the tide waves.
Unit of space of a tide wave.
When Earth, Moon and Sun are aligned.
Different tide cadences.

Code proposition: [P0] neutral; [P1] classic theory; [P2] favouring the inductive approach; [P3] inductive approach.


[P3] Let us limit ourselves to consider the ratio between the attraction of the Earth on the water of its oceans, and the attraction of the Moon on the same water.

The Earth attracts its waters nine million times more than the Moon.

[P2] The ratio is 1 : 1,14 x 1O-7.
[[in "ocean" Encyclopædia Britannica Online.
[Accessed September 1 1999]].

[P3] A question: how is it possible that such a tiny value of attraction by the Moon counteracts the attraction by the Earth, with a considerable effect?

[P1] The attraction of the Moon would be entirely insufficient to "lift" the water of our oceans - because it is about one 9 millionth part of the force of earth-gravity. However ...

The horizontal component.

[P1] ..., while the vertical component is negligeable, the horizontal one has the effective role to attract the waters of seas and oceans westward.

Since the horizontal component is not opposed by the Earth gravity [sic!], the two tidal waves move westbound, from a meridian to the successive one.

[P3] Indeed, thanks to satellites, we know that there are several tidal waves, one for each tidal basin; each of them does not move westwards, from a meridian to the successive one, but in a roughly circular way, within its own basin (see page 4.6).